Phase change random access memory device

ABSTRACT

A memory device includes: a first conductive column structure extending through a first dielectric layer, wherein the first conductive column structure comprises a shell portion wrapping a core structure filled with a dielectric material and an end portion that is coupled to one end of the shell portion and disposed below the core structure; and a first phase change material layer formed over the first dielectric layer, wherein a lower boundary of the first phase change material layer contacts at least a first portion of the other end of the shell portion of the first conductive column structure.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to U.S. Provisional PatentApplication No. 62/591,318, filed on Nov. 28, 2018, which isincorporated by reference herein in its entirety.

BACKGROUND

In recent years, unconventional nonvolatile memory (NVM) devices, suchas ferroelectric random access memory (FRAM) devices, resistive randomaccess memory (RRAM) devices, and phase change random access memory(PCRAM) devices have emerged. In particular, PCRAM devices, whichexhibit a switching behavior between a high resistance state and a lowresistance state, have various advantages over conventional NVM devices.Such advantages include, for example, compatible fabrication steps withcurrent complementary-metal-oxide-semiconductor (CMOS) technologies,low-cost fabrication, a compact structure, flexible scalability, fastswitching, high integration density, etc.

Generally, a PCRAM device includes a top electrode (e.g., an anode) anda bottom electrode (e.g., a cathode) with a phase change material layerinterposed therebetween. Further, the bottom electrode is coupled to thephase change material layer with a conductive structure, typically knowsas a “heater” structure. To transition the PCRAM device to the lowresistance state, which is typically referred to as a set operation, arelatively low electrical current signal is applied on the phase changematerial layer through the heater structure to anneal the phase changematerial layer at a temperature between respective crystallization(lower) and melting (higher) temperatures of the phase change materiallayer so as to crystallize the phase change material layer; and totransition the PCRAM device to the high resistance state, which istypically referred to as a reset operation, a relatively high electricalcurrent signal is applied on the phase change material layer via theheater structure to anneal the phase change material layer at atemperature higher than the melting (higher) temperature of the phasechange material layer so as to amorphorize the phase change materiallayer. In particular, a current level of the applied electrical currentsignal that can successfully amorphorize/crystallize the phase changematerial layer is proportional to a contact area size at an interfacebetween the heater structure and the phase change material layer. Forexample, the bigger the contact area size is, the higher the currentlevel of the applied electrical current signal needs to be.

The heater structures of existing PCRAM devices, however, couplerespective phase change material layers with relatively large contactareas, which disadvantageously requires respective current levels to berelatively high. Various issues may accordingly occur in exiting PCRAMdevices when applying such a high current level signal, for example,less reliability, higher power consumption, etc. Thus, existing PCRAMdevices and methods to make the same are not entirely satisfactory.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that various features are not necessarily drawn to scale. In fact,the dimensions and geometries of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIGS. 1A and 1B illustrate a flow chart of an exemplary method forforming a semiconductor device, in accordance with some embodiments.

FIG. 2A, 2B, 2C, 2D, 2E, 2F, 2G, 2H, 2I, 2J, 2K, 2L, 2M, 2N, and 2Oillustrate cross-sectional views of an exemplary semiconductor deviceduring various fabrication stages, made by the method of FIG. 1, inaccordance with some embodiments.

FIGS. 3A, 3B, 3C, 3D, 3E, and 3F illustrate respective plan views ofvarious embodiments of part of the exemplary semiconductor device madeby the method of FIG. 1, in accordance with some embodiments.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following disclosure describes various exemplary embodiments forimplementing different features of the subject matter. Specific examplesof components and arrangements are described below to simplify thepresent disclosure. These are, of course, merely examples and are notintended to be limiting. For example, the formation of a first featureover or on a second feature in the description that follows may includeembodiments in which the first and second features are formed in directcontact, and may also include embodiments in which additional featuresmay be formed between the first and second features, such that the firstand second features may not be in direct contact. In addition, thepresent disclosure may repeat reference numerals and/or letters in thevarious examples. This repetition is for the purpose of simplicity andclarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The present disclosure provides various embodiments of a novel PCRAM(phase change random access memory) device and methods to form the same.In some embodiments, the disclosed PCRAM device includes a bottomelectrode, a bottom conductive column structure, a phase change materiallayer, an optional top conductive column structure, and a top electrode,wherein the bottom and top conductive column structures each includes asidewall portion formed as a “shell” structure surrounding a “core”structure formed of a dielectric material. Specifically, the bottomelectrode is coupled to the phase change material layer through thesidewall portion of the bottom conductive column structure, and the topelectrode is coupled to the phase change material layer through the topconductive column structure. In some embodiments, the bottom and topconductive column structures may be each configured to conduct a currentsignal to the phase change material layer. Since the sidewall portion ofthe bottom conductive column structure is formed as the shell structure,a corresponding contact area size at the interface between the phasechange material layer and the bottom conductive column structure can besignificantly reduced when compared to the conventional PCRAM devices.As such, various issues that the conventional PCRAM devices encountercan be advantageously avoided in disclosed PCRAM devices.

FIGS. 1A and 1B illustrate a flowchart of a method 100 to form asemiconductor device according to one or more embodiments of the presentdisclosure. It is noted that the method 100 is merely an example, and isnot intended to limit the present disclosure. In some embodiments, thesemiconductor device is, at least part of, a PCRAM device. As employedby the present disclosure, the PCRAM device refers to any deviceincluding a phase change material layer. It is noted that the method 100of FIGS. 1A and 1B does not produce a completed PCRAM device. Acompleted PCRAM device may be fabricated using complementarymetal-oxide-semiconductor (CMOS) technology processing. Accordingly, itis understood that additional operations may be provided before, during,and after the method 100 of FIGS. 1A and 1B, and that some otheroperations may only be briefly described herein. In some otherembodiments, the method may be used to form any of a variety ofnonvolatile memory (NVM) devices, such as ferroelectric random accessmemory (FRAM) devices, resistive random access memory (RRAM) devices,etc., while remaining within the scope of the present disclosure.

Referring first to FIG. 1A, in some embodiments, the method 100 startswith operation 102 in which a substrate including a transistor isprovided. The method 100 continues to operation 104 in which a firstdielectric layer including a contact plug extending therethrough isformed over the substrate. In some embodiments, the first dielectriclayer is formed over the transistor, and the contact plug iselectrically coupled to at least one conductive feature (e.g., a drain,source, or a gate feature) of the transistor. The method 100 continuesto operation 106 in which a second dielectric layer is formed over thefirst dielectric layer. The method 100 continues to operation 108 inwhich a first electrode is formed in the second dielectric layer. Insome embodiments, the first electrode is electrically coupled to thecontact plug extending through the first dielectric layer. The method100 continues to operation 110 in which a third dielectric layer isformed over the second dielectric layer.

Next, the method 100 continues to operation 112 in which a portion ofthe third dielectric layer is etched to form a trench extending throughthe third dielectric layer so as to expose a portion of an upperboundary of the first electrode. The method 100 continues to operation114 in which an isolation layer is formed over the etched thirddielectric layer to line the trench. As such, the isolation layerextends along sidewalls of the trench and overlays a bottom boundary ofthe trench (i.e., the portion of the upper boundary of the firstelectrode that was exposed in operation 112). It is noted that in someembodiments, the isolation layer may also overlay an upper boundary ofthe third dielectric layer. The method 100 continues to operation 116 inwhich a portion the isolation layer is etched to re-expose the portionof the upper boundary of the first electrode. In some embodiments,concurrently with the exposure of the portion of the upper boundary ofthe first electrode, another portion of the isolation that overlays theupper boundary of the third dielectric layer is also etched away.

Referring then to FIG. 1B, the method 100 continues to operation 118 inwhich a conductive layer is formed over the etched third dielectriclayer to line the trench. Specifically, in some embodiments, theconductive layer is formed to overlay the re-exposed portion of theupper boundary of the first electrode, extend along sidewalls of thetrench (with the isolation layer coupled therebetween), and overlays theupper boundary of the third dielectric layer. The method 100 continuesto operation 120 in which a dielectric material is formed over theetched third dielectric layer to fill the trench. Specifically, in someembodiments, the dielectric material fills the trench with the isolationlayer and the conductive layer disposed therebetween. The method 100continues to operation 122 in which a polishing process is performed toform a first conductive column structure. In some embodiments, thepolishing process (e.g., a chemical mechanical polishing (CMP) process)is performed on the dielectric material and the conductive layer untilan upper boundary of a sidewall portion of the conductive layer isexposed, which accordingly forms the first conductive column structure.As such, the first conductive column structure includes at least twoportions: a first portion that is the portion of the conductive layeroverlaying the upper boundary of the first electrode; and a secondportion that is the sidewall portion of the conductive layer.

Next, the method 100 continues to operation 124 in which a phase changematerial layer is formed over the first conductive column structure. Insome embodiments, the phase change material layer is formed to couple atleast the upper boundary of the sidewall portion of the conductive layer(the first conductive column structure). The method 100 continues tooperation 126 in which a fourth dielectric layer is formed over thephase change material layer. The method 100 continues to operation 128in which a second conductive column structure is formed to couple thephase change material layer. In some embodiments, the second conductivecolumn structure, which may be optionally formed in the fourthdielectric layer, is substantially similar to the first conductivecolumn structure. The method 100 continues to operation 130 in which asecond electrode is formed to couple the second conductive columnstructure. In some embodiments, the second electrode, which may beformed in a fifth dielectric layer over the fourth dielectric layer, issubstantially similar to the first electrode. In some embodiments, theabove-mentioned first, second, third, fourth, and fifth dielectriclayers may each be an inter-metal dielectric (IMD) or inter-layerdielectric (ILD) layer, that is, the first, second, third, fourth, andfifth dielectric layers may be formed of a substantially similardielectric material (e.g., low-k dielectric material).

In some embodiments, operations of the method 100 may be associated withcross-sectional views of a semiconductor device 200 at variousfabrication stages as shown in FIGS. 2A, 2B, 2C, 2D, 2E, 2F, 2G, 2H, 2I,2J, 2K, 2L, 2M, 2N, and 2O, respectively. In some embodiments, thesemiconductor device 200 may be a PCRAM device. The PCRAM device 200 maybe included in a microprocessor, memory cell, and/or other integratedcircuit (IC). Also, FIGS. 2A through 2O are simplified for a betterunderstanding of the concepts of the present disclosure. For example,although the figures illustrate the PCRAM device 200, it is understoodthe IC, in which the PCRAM device 200 is formed, may include a number ofother devices comprising resistors, capacitors, inductors, fuses, etc.,which are not shown in FIGS. 2A through 2O, for purposes of clarity ofillustration.

Corresponding to operation 102 of FIG. 1A, FIG. 2A is a cross-sectionalview of the PCRAM device 200 including a substrate 202 with a transistor204, which is provided at one of the various stages of fabrication,according to some embodiments. Although the PCRAM device 200 in theillustrated embodiment of FIG. 2A includes only one transistor 204, itis understood that the illustrated embodiment of FIG. 2A and thefollowing figures are merely provided for illustration purposes. Thus,the PCRAM device 200 may include any desired number of transistors whileremaining within the scope of the present disclosure.

In some embodiments, the substrate 202 includes a semiconductor materialsubstrate, for example, silicon. Alternatively, the substrate 202 mayinclude other elementary semiconductor material such as, for example,germanium. The substrate 202 may also include a compound semiconductorsuch as silicon carbide, gallium arsenic, indium arsenide, and indiumphosphide. The substrate 202 may include an alloy semiconductor such assilicon germanium, silicon germanium carbide, gallium arsenic phosphide,and gallium indium phosphide. In one embodiment, the substrate 202includes an epitaxial layer. For example, the substrate may have anepitaxial layer overlying a bulk semiconductor. Furthermore, thesubstrate 202 may include a semiconductor-on-insulator (SOI) structure.For example, the substrate may include a buried oxide (BOX) layer formedby a process such as separation by implanted oxygen (SIMOX) or othersuitable technique, such as wafer bonding and grinding.

In some embodiments, the transistor 204 includes a gate electrode 204-1,a gate dielectric layer 204-2, and source/drain features 204-3 and204-4. The source/drain features 204-3 and 204-4 may be formed usingdoping processes such as ion implantation. The gate dielectric layer204-2 may include a dielectric material such as, silicon oxide, siliconnitride, silicon oxinitride, dielectric with a high dielectric constant(high-k), and/or combinations thereof, which may be formed usingdeposition processes such as atomic layer deposition (ALD). The gateelectrode 204-1 may include a conductive material, such as polysiliconor a metal, which may be formed using deposition processes such aschemical vapor deposition (CVD). In some embodiments, the transistor 204may serve as an access transistor of the PCRAM device 200, whichcontrols an access to a data storage component (e.g., a PCRAM resistor)of the PCRAM device 200 during read/write operations.

Corresponding to operation 104 of FIG. 1A, FIG. 2B is a cross-sectionalview of the PCRAM device 200 including a first dielectric layer 208 witha contact plug 210, which is formed at one of the various stages offabrication, according to some embodiments. As shown, the firstdielectric layer 208 is formed over the transistor 204, and the contactplug 210 is formed to extend through the first dielectric layer 206. Insome embodiments, the contact plug 210 is coupled to at least one of theconductive features of the transistor 204. In the illustrated embodimentof FIG. 2B (and the following figures), the contact plug 210 is coupledto the source/drain feature 204-3.

In some embodiments, the first dielectric layer 208 is formed of adielectric material. Such a dielectric material may include at least oneof: silicon oxide, a low dielectric constant (low-k) material, othersuitable dielectric material, or a combination thereof. The low-kmaterial may include fluorinated silica glass (FSG), phosphosilicateglass (PSG), borophosphosilicate glass (BPSG), carbon doped siliconoxide (SiO_(x)C_(y)), strontium oxide (SrO), Black Diamond® (AppliedMaterials of Santa Clara, Calif.), Xerogel, Aerogel, amorphousfluorinated carbon, Parylene, BCB (bis-benzocyclobutenes), SiLK (DowChemical, Midland, Mich.), polyimide, and/or other future developedlow-k dielectric materials. In some embodiments, the contact plug 210 isformed of a conductive material such as, for example, copper (Cu),aluminum (Al), tungsten (W), etc.

The contact plug 210 may be formed by at least some of the followingprocess steps: using chemical vapor deposition (CVD), physical vapordeposition (PVD), spin-on coating, and/or other suitable techniques todeposit the above-described dielectric material of the first dielectriclayer 208 over the substrate 202 and the transistor 204; performing oneor more patterning processes (e.g., a lithography process, a dry/wetetching process, a cleaning process, a soft/hard baking process, etc.)to form an opening through the dielectric material; using CVD, PVD,E-gun, and/or other suitable techniques to deposit the above-describedconductive material to refill the opening; and polishing out excessiveconductive material to form the contact plug 210.

Corresponding to operation 106 of FIG. 1A, FIG. 2C is a cross-sectionalview of the PCRAM device 200 including a second dielectric layer 212,which is formed at one of the various stages of fabrication, accordingto some embodiments. As shown, the second dielectric layer 212 is formedover the first dielectric layer 208 and the contact plug 210.

In some embodiments, the second dielectric layer 212 is formed of adielectric material. Such a dielectric material may include at least oneof: silicon oxide, a low dielectric constant (low-k) material, othersuitable dielectric material, or a combination thereof. The low-kmaterial may include fluorinated silica glass (FSG), phosphosilicateglass (PSG), borophosphosilicate glass (BPSG), carbon doped siliconoxide (SiO_(x)C_(y)), strontium oxide (SrO), Black Diamond® (AppliedMaterials of Santa Clara, Calif.), Xerogel, Aerogel, amorphousfluorinated carbon, Parylene, BCB (bis-benzocyclobutenes), SiLK (DowChemical, Midland, Mich.), polyimide, and/or other future developedlow-k dielectric materials. The second dielectric layer 212 may beformed by using chemical vapor deposition (CVD), physical vapordeposition (PVD), spin-on coating, and/or other suitable techniques todeposit the above-described dielectric material of the second dielectriclayer 212 over the first dielectric layer 208.

Corresponding to operation 108 of FIG. 1A, FIG. 2D is a cross-sectionalview of the PCRAM device 200 including a first electrode 214, which isformed at one of the various stages of fabrication, according to someembodiments. As shown, the first electrode 214 is embedded in the seconddielectric layer 212 and horizontally extends along the seconddielectric layer 212. In some embodiments, the first electrode 214 iscoupled to the contact plug 210, and as will be discussed below, thefirst electrode 212 may serve as a bottom electrode of the data storagecomponent (e.g., a PCRAM resistor) of the PCRAM device 200.

In some embodiments, the first electrode 214 is formed of a conductivematerial such as, for example, copper (Cu), aluminum (Al), tungsten (W),etc. The first electrode 214 may be formed by at least some of thefollowing process steps: performing one or more patterning processes(e.g., a lithography process, a dry/wet etching process, a cleaningprocess, a soft/hard baking process, etc.) to form an opening throughthe second dielectric layer 212 so as to expose at least a portion ofthe contact plug 210; using CVD, PVD, E-gun, and/or other suitabletechniques to deposit the above-described conductive material to refillthe opening; and polishing out excessive conductive material to form thefirst electrode 214.

Corresponding to operation 110 of FIG. 1A, FIG. 2E is a cross-sectionalview of the PCRAM device 200 including a third dielectric layer 216,which is formed at one of the various stages of fabrication, accordingto some embodiments. As shown, the third dielectric layer 216 is formedover the second dielectric layer 212 and the first electrode 214.

In some embodiments, the third dielectric layer 216 is formed of adielectric material. Such a dielectric material may include at least oneof: silicon oxide, a low dielectric constant (low-k) material, othersuitable dielectric material, or a combination thereof. The low-kmaterial may include fluorinated silica glass (FSG), phosphosilicateglass (PSG), borophosphosilicate glass (BPSG), carbon doped siliconoxide (SiO_(x)C_(y)), strontium oxide (SrO), Black Diamond® (AppliedMaterials of Santa Clara, Calif.), Xerogel, Aerogel, amorphousfluorinated carbon, Parylene, BCB (bis-benzocyclobutenes), SiLK (DowChemical, Midland, Mich.), polyimide, and/or other future developedlow-k dielectric materials. The third dielectric layer 216 may be formedby using chemical vapor deposition (CVD), physical vapor deposition(PVD), spin-on coating, and/or other suitable techniques to deposit theabove-described dielectric material of the third dielectric layer 216over the second dielectric layer 212.

Corresponding to operation 112 of FIG. 1A, FIG. 2F is a cross-sectionalview of the PCRAM device 200 in which a portion of the third dielectriclayer 216 is etched at one of the various stages of fabrication,according to some embodiments. As shown, after the portion of the thirddielectric layer 216 is etched, a trench, or void, 218 that extendsthrough the third dielectric layer 216 is formed. Accordingly, in someembodiments, the trench 218 exposes inner sidewalls 216′ of the thirddielectric layer 216 and at least a portion of an upper boundary 214′ ofthe first electrode 214.

In some embodiments, the trench 218 is formed by performing at leastsome of the following process steps: performing one or more patterningprocesses (e.g., a lithography process, a dry/wet etching process, acleaning process, a soft/hard baking process, etc.) to form apatternable layer with an opening over the third dielectric layer 216,wherein the opening is laterally aligned with at least a portion of theupper boundary 214′ of the first electrode 214; performing one or moredry/wet etching process on the third dielectric layer 216 while usingthe patternable layer as a mask until the portion of the upper boundary214′ is exposed; and removing the patternable layer.

Corresponding to operation 114 of FIG. 1A, FIG. 2G is a cross-sectionalview of the PCRAM device 200 including an isolation layer 222, which isformed at one of the various stages of fabrication, according to someembodiments. As shown, the isolation layer 222 is formed to overlay anupper boundary 216″ of the third dielectric layer 216, and line thetrench 218 (i.e., extending along the sidewalls 216′ and overlaying theupper boundary 214′). In some embodiments, the isolation layer 222 issubstantially thin and conformal so that the profile of the trench 218may remain present after the formation of the isolation layer 222.

In some embodiments, the isolation layer 222 is formed of a dielectricmaterial, for example, silicon oxide, silicon nitride, or the like. Theisolation layer 222 may be formed by using chemical vapor deposition(CVD), physical vapor deposition (PVD), spin-on coating, and/or othersuitable techniques to deposit the above-described dielectric materialof the isolation layer 222 over the etched third dielectric layer 216.

Corresponding to operation 116 of FIG. 1A, FIG. 2H is a cross-sectionalview of the PCRAM device 200 in which an etching process 223 isperformed at one of the various stages of fabrication, according to someembodiments. According to some embodiments, the etching process 223 maybe an anisotropic etching process (e.g., a reactive ion etching (RIE)process). Thus, concurrently with or subsequently to the etching process223, portions of the isolation layer 222 that overlay the upperboundaries 214′ of the first electrode 214 and 216″ of the thirddielectric layer 216, respectively, are removed, which leaves sidewallportions 222-1 of the isolation layer 222 intact. As shown in theillustrated embodiment of FIG. 2H (and the following figures), thesidewall portions 222-1 extends along the sidewall 216′ of the thirddielectric layer 216.

Corresponding to operation 118 of FIG. 1B, FIG. 2I is a cross-sectionalview of the PCRAM device 200 including a conductive layer 224, which isformed at one of the various stages of fabrication, according to someembodiments. As shown, the conductive layer 224 is formed to line thetrench 218 and overlay the upper boundary 216″. More specifically, theconductive layer 224 lines the trench 218 by extending along thesidewall portions 222-1 of the isolation layer 222 with respectivesidewall portions 224-1 and overlaying the upper boundary 214′ of thefirst electrode 214 with a bottom portion 224-2. In some embodiments,the conductive layer 224 is substantially thin and conformal (e.g., 1nanometers to 10 nanometers) so that the profile of the trench 218 mayremain present after the formation of the conductive layer 224.

Although in FIG. 2I (and the following figures), the conductive layer224 is illustrated as a single layer, it is understood that theconductive layer 224 may include two or more layers stacked on the topof one another, each of which may be formed of a conductive materialsuch as, for example, gold (Au), platinum (Pt), ruthenium (Ru), iridium(Ir), titanium (Ti), aluminum (Al), copper (Cu), tantalum (Ta), tungsten(W), iridium-tantalum alloy (Ir—Ta), indium-tin oxide (ITO), or anyalloy, oxide, nitride, fluoride, carbide, boride or silicide of these,such as TaN, TiN, TiAlN, TiW, or a combination thereof. In someembodiments, the first conductive layer 224 is formed by using chemicalvapor deposition (CVD), plasma enhanced (PE) CVD, high-density plasma(HDP) CVD, inductively-coupled-plasma (ICP) CVD, physical vapordeposition (PVD), spin-on coating, and/or other suitable techniques todeposit the at least one of the above-described conductive material overthe etched third dielectric layer 216 and the sidewall portions 222-1 ofthe isolation layer 222.

Corresponding to operation 120 of FIG. 1B, FIG. 2J is a cross-sectionalview of the PCRAM device 200 including a dielectric material 228, whichis deposited at one of the various stages of fabrication, according tosome embodiments. As shown, the dielectric material 228 is formed tooverlay the conductive layer 224, which accordingly fills the trench 218with the dielectric material 228.

In some embodiments, the dielectric material 228 is formed of asubstantially similar dielectric material as the third dielectric layer216. Such a dielectric material may include at least one of: siliconoxide, a low dielectric constant (low-k) material, other suitabledielectric material, or a combination thereof. The low-k material mayinclude fluorinated silica glass (FSG), phosphosilicate glass (PSG),borophosphosilicate glass (BPSG), carbon doped silicon oxide(SiO_(x)C_(y)), strontium oxide (SrO), Black Diamond® (Applied Materialsof Santa Clara, Calif.), Xerogel, Aerogel, amorphous fluorinated carbon,Parylene, BCB (bis-benzocyclobutenes), SiLK (Dow Chemical, Midland,Mich.), polyimide, and/or other future developed low-k dielectricmaterials. The dielectric material 228 may be formed by using chemicalvapor deposition (CVD), physical vapor deposition (PVD), spin-oncoating, and/or other suitable techniques to deposit the above-describeddielectric material over the conductive layer 224.

Corresponding to operation 122 of FIG. 1B, FIG. 2K is a cross-sectionalview of the PCRAM device 200 including a first conductive columnstructure 230, which is formed at one of the various stages offabrication, according to some embodiments. According to someembodiments, the first conductive column structure 230 is formed byperforming at least one CMP process on the dielectric material 228 andthe conductive layer 224 disposed thereunder (FIG. 2J) until respectiveupper boundaries 225 of the sidewall portions 222-1 are exposed.Accordingly, a remaining portion 228′ of the dielectric material 228 issurrounded by the sidewall portions 224-1 and bottom portion 224-2 ofthe conductive layer 224 at its sidewalls and a bottom boundary, whichexposes a respective upper boundary 229. In other words, the firstconductive column structure 230 may include a first portion 224-1 formedas a shell structure (hereinafter “shell portion 224-1”) surrounding theremaining portion 228′ formed as a core structure, and a second portion224-2 coupled to one end of such a shell structure (hereinafter “endportion 224-2”).

Corresponding to operation 124 of FIG. 1B, FIG. 2L is a cross-sectionalview of the PCRAM device 200 including a phase change material layer232, which is formed at one of the various stages of fabrication,according to some embodiments. As shown, the phase change material layer232 is formed over the etched third dielectric layer 216 to couple atleast part of the first conductive column structure 230. In theillustrated embodiment of FIG. 2L, the phase change material layer 232is coupled to both the shell portions 224-1 of the first conductivecolumn structure 230. More specifically, the phase change material layer232 overlays both the boundaries 225 of the shell portions 224-1. Insome other embodiments, the phase change material layer 232 may be onlycoupled to part of the shell portions 224-1 (e.g., one of the shellportions 224-1), which will be illustrated and discussed below withrespect to FIGS. 3A-3F.

In some embodiments, the phase change material layer 232 includes achalcogenide-based material. Chalcogens include any of the four elementsoxygen (O), sulfur (S), selenium (Se), and tellurium (Te), forming partof group VI of the periodic table. Chalcogenides comprise compounds of achalcogen with a more electropositive element or radical. Chalcogenidealloys comprise combinations of chalcogenides with other materials suchas transition metals. A chalcogenide alloy usually contains one or moreelements from column six of the periodic table of elements, such asgermanium (Ge) and tin (Sn). For example, chalcogenide alloys includecombinations including one or more of antimony (Sb), gallium (Ga),indium (In), and silver (Ag). Exemplary materials of the phase changematerial layer 232 include alloys of: Ga/Sb, In/Sb, In/Se, Sb/Te, Ge/Te,Ge/Sb/Te, In/Sb/Te, Ga/Se/Te, Sn/Sb/Te, In/Sb/Ge, Ag/In/Sb/Te,Ge/Sn/Sb/Te, Ge/Sb/Se/Te and Te/Ge/Sb/S.

In some embodiments, the phase change material layer 232 may be formedby an atomic layer deposition (ALD) technique with a precursorcontaining a metal and oxygen. In some embodiments, other chemical vapordeposition (CVD) techniques may be used. In some embodiments, the phasechange material layer 232 may be formed by a physical vapor deposition(PVD) technique, such as a sputtering process with a metallic target andwith a gas supply of oxygen and optionally nitrogen to the PVD chamber.In some embodiments, the phase change material layer 232 may be formedby an electron-beam deposition technique.

Corresponding to operation 126 of FIG. 1B, FIG. 2M is a cross-sectionalview of the PCRAM device 200 including a fourth dielectric layer 234,which is formed at one of the various stages of fabrication, accordingto some embodiments. As shown, the fourth dielectric layer 234 is formedover the etch third dielectric layer 216 to overlay the phase changematerial layer 232.

In some embodiments, the fourth dielectric layer 234 is formed of adielectric material. Such a dielectric material may include at least oneof: silicon oxide, a low dielectric constant (low-k) material, othersuitable dielectric material, or a combination thereof. The low-kmaterial may include fluorinated silica glass (FSG), phosphosilicateglass (PSG), borophosphosilicate glass (BPSG), carbon doped siliconoxide (SiO_(x)C_(y)), strontium oxide (SrO), Black Diamond® (AppliedMaterials of Santa Clara, Calif.), Xerogel, Aerogel, amorphousfluorinated carbon, Parylene, BCB (bis-benzocyclobutenes), SiLK (DowChemical, Midland, Mich.), polyimide, and/or other future developedlow-k dielectric materials. The fourth dielectric layer 234 may beformed by using chemical vapor deposition (CVD), physical vapordeposition (PVD), spin-on coating, and/or other suitable techniques todeposit the above-described dielectric material of the fourth dielectriclayer 234 over the etched third dielectric layer 216 and the phasechange material layer 232.

Corresponding to operation 128 of FIG. 1B, FIG. 2N is a cross-sectionalview of the PCRAM device 200 including a second conductive columnstructure 240, which is formed at one of the various stages offabrication, according to some embodiments. As shown, the secondconductive structure 240 extends through part of the fourth dielectriclayer 234 to couple the phase change material layer 232.

In some embodiments, the second conductive column structure 240 issubstantially similar to the first conductive column structure 230 sothat the configuration of the second conductive column structure 240 isbriefly discussed below, and the formation of the second conductivecolumn structure 240 is not repeated here. The second conductive columnstructure 240 also includes a shell portion 242-1 surrounding a corestructure formed of a remaining portion 241 of a dielectric material(similar as the dielectric material 228 of FIG. 2J), and an end portion242-2 coupled to one end of the shell portion 242-1. As such, the secondconductive column structure 240 is coupled to the phase change materiallayer 232 via the end portion 242-2, and to the fourth dielectric layer234 via the sidewall portion 242-1 with an isolation layer 242-1disposed therebetween. In some embodiments, the isolation layer 242-1 issubstantially similar to the sidewall portion 222-1. Further, althoughin the illustrated embodiment of FIG. 2N the second conductive columnstructure 240 is aligned with the first conductive column structure 230,it is noted that the second conductive column structure 240 may belaterally shifted from the first conductive column structure 230 (aslong as the second conductive column structure 240 is still coupled tothe phase change material layer 232) while remaining within the scope ofthe present disclosure.

Corresponding to operation 130 of FIG. 1B, FIG. 2O is a cross-sectionalview of the PCRAM device 200 including a second electrode 244, which isformed at one of the various stages of fabrication, according to someembodiments. As shown, the second electrode 244 is embedded in a fifthdielectric layer 246 and horizontally extends along the fifth dielectriclayer 246. In some embodiments, the second electrode 244 is coupled tothe second conductive column structure 240, and as will be discussedbelow, the second electrode 212 may serve as a top electrode of the datastorage component (e.g., a PCRAM resistor) of the PCRAM device 200.

In some embodiments, the second electrode 244 is formed of a conductivematerial such as, for example, copper (Cu), aluminum (Al), tungsten (W),etc. The second electrode 244 may be formed by at least some of thefollowing process steps: performing one or more patterning processes(e.g., a lithography process, a dry/wet etching process, a cleaningprocess, a soft/hard baking process, etc.) to form an opening throughthe fifth dielectric layer 246 so as to expose at least a portion of thesecond conductive column structure 240; using CVD, PVD, E-gun, and/orother suitable techniques to deposit the above-described conductivematerial to refill the opening; and polishing out excessive conductivematerial to form the second electrode 244. It is noted that in someembodiments, each of the above-described first/second/third/fourth/fifthdielectric layers (208/212/216/234/246) may be an inter-metal dielectric(IMD) or inter-layer dielectric (ILD) layer.

In some embodiments, after the formation of the second electrode 244, aPCRAM resistor of the PCRAM device 200 may be formed. More specifically,the first electrode 214 may serve as the bottom electrode of the PCRAMresistor, the first conductive column structure 230 may serves as theheater structure of the PCRAM resistor, the phase change material layer232 may be configured to switch between the low and high resistancestates by being transitioned to the partially crystalline and amorphousstates, respectively, the second conductive column structure 240 mayserve as an optional heater structure of the PCRAM resistor, and thesecond electrode 244 may serve as the top electrode.

In operation, the PCRAM device 200 may be “granted” to be accessedthrough the access transistor 204. Upon accessed, the PCRAM device 200may transition between the low and high resistance states through setand reset operations, respectively, as discussed above. When compared tothe conventional PCRAM devices, a contact area size between the heaterstructure (e.g., the first conductive column structure 230) and thephase change material layer 232 is significantly reduced. Specifically,in the illustrated embodiment of FIG. 2O, the contact area size may bedefined as twice the cross-sectional area of the shell portion 224-1(i.e., the thickness of the conductive layer 224, as described withrespect to FIG. 2I), which is significantly smaller than the contactarea size of the conventional PCRAM devices that typically includesadditional cross-sectional area of the remaining portion 228′.Accordingly, the current level of an electrical current signal appliedto transition the resistance states of the phase change material layer232 can be advantageously reduced, which avoids various issues that theconventional PCRAM device are facing.

FIGS. 3A, 3B, 3C, 3D, 3E, and 3F respectively illustrate top views ofvarious embodiments of how the first conductive column structure 230that extends through the dielectric layer 216 is spatially configuredwith respect to the phase change material layer 232 that is disposed inanother dielectric layer above the dielectric layer 216. As will bediscussed below, the shell portion 224-1 of the first conductive columnstructure 230 may be formed as a circular or polygonal ring when viewedfrom the top; the phase change material layer 232 may be formed to havecircular shape, a polygonal shape, or a circumferential shape whenviewed from the top; and the phase change material layer 232 may bepartially overlapped with (i.e., coupled to) a portion of the shellportion 224-1 of the first conductive column structure 230.

For example, in FIG. 3A, the shell portion 224-1 is formed as arectangular ring that surrounds the remaining portion 228′ of thedielectric material 228. Alternatively stated, the shell portion 224-1has an inner boundary and an outer boundary that each form acircumference of a rectangle shape. And the phase change material layer232, formed as a rectangular shape, overlaps (e.g., contacts) part ofsuch a rectangular ring. Accordingly, a corresponding contact area sizemay be defined as a cross-sectional area of overlapping 301 enclosed bydotted lines. In FIG. 3B, the shell portion 224-1 is formed as arectangular ring that is substantially similar to the one shown in FIG.3A, but the phase change material layer 232, also formed as arectangular shape, overlaps the shell portion 224-1 by a smaller area (across-sectional area of overlapping 303 enclosed by dotted lines).

In FIG. 3C, the shell portion 224-1 is formed as a circular ringsurrounds the remaining portion 228′ of the dielectric material 228.Alternatively stated, the shell portion 224-1 has an inner boundary andan outer boundary that each form a circumference of a circular shape.And the phase change material layer 232, formed as a rectangular ring(e.g., a circumferential shape), overlaps part of such a circular ring.Accordingly, a corresponding contact area size may be defined as across-sectional area of overlapping 305 enclosed by dotted lines.

In FIG. 3D, the shell portion 224-1 is faulted as a first circular ringsurrounds the remaining portion 228′ of the dielectric material 228, andthe phase change material layer 232 (enclosed by dotted lines) is formedas a second circular ring. Further, in some embodiments, such a firstcircular ring (the shell portion 224-1) may overlap with the secondcircular ring (the phase change material layer 232) by running along acircumference of the second circular ring, which defines an overlapping(not shown) that is part of the cross-sectional area of either the firstor second circular ring.

In FIG. 3E, the shell portion 224-1 is formed as a rectangular ring andthe phase change material layer 232 is formed as a rectangular shape,which is similar to FIGS. 3A and 3B, except that the phase changematerial layer 232 may be formed to have two or more respectivedifferent portions. For example, in the illustrated embodiment of FIG.3E, the phase change material layer 232 includes a first portion 232-1and a second portion 232-2 that are laterally spaced apart from eachother and respectively overlapped with the rectangular ring of the shellportion 224-1.

In FIG. 3F, the shell portion 224-1 is formed as a circular ring and thephase change material layer 232 is formed to have two rectangle shapesthat are laterally spaced apart from each other. For example, in theillustrated embodiment of FIG. 3F, the phase change material layer 232includes a first portion 232-3 and a second portion 232-4 that arerespectively overlapped with the circular ring of the shell portion224-1.

In an embodiment, a memory device includes: a first conductive columnstructure extending through a first dielectric layer, wherein the firstconductive column structure comprises a shell portion wrapping a corestructure filled with a dielectric material and an end portion that iscoupled to one end of the shell portion and disposed below the corestructure; and a first phase change material layer formed over the firstdielectric layer, wherein a lower boundary of the first phase changematerial layer contacts at least a first portion of the other end of theshell portion of the first conductive column structure.

In another embodiment, a memory device includes: a bottom electrode; aphase change material layer; and a heater structure, coupled between thebottom electrode and the phase change material layer, that lines atrench thereby causing a first portion of the heater structure tocontact the phase change material layer at one end and wrap a dielectricmaterial directly disposed below the phase change material layer.

Yet in another embodiment, a method includes: forming a first dielectriclayer over a bottom electrode; forming a first void extending throughthe first dielectric layer to expose a portion of an upper boundary ofthe bottom electrode; forming a first conductive structure lining alongrespective sidewalls of the first void and the exposed portion of theupper boundary of the bottom electrode; filling the first void with thefirst dielectric layer; and forming a phase change material layer overthe first dielectric layer to cause the phase change material layer tocontact at least a portion of a sidewall of the first conductivestructure.

The foregoing outlines features of several embodiments so that thoseordinary skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodimentsintroduced herein. Those skilled in the art should also realize thatsuch equivalent constructions do not depart from the spirit and scope ofthe present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A memory device, comprising: a first conductivecolumn structure extending entirely through a first dielectric layer,wherein the first conductive column structure comprises a shell portionwrapping a core structure filled with a dielectric material and an endportion that is coupled to a first end of the shell portion and disposedbelow the core structure, wherein the shell portion comprises aconductive layer; a first phase change material layer formed over thefirst dielectric layer, wherein a lower boundary of the first phasechange material layer contacts at least a first portion of a second endof the shell portion, the second end being opposite the first end; asecond dielectric layer disposed above the first phase change materiallayer; and a second conductive column structure extending through thesecond dielectric layer, wherein the second conductive column structurecomprises a shell portion wrapping a core structure filled with adielectric material and an end portion that is coupled to one end of theshell portion and disposed below the core structure, wherein an upperboundary of the first phase change material layer contacts the endportion of the second conductive column.
 2. The memory device of claim1, further comprising: a bottom electrode disposed below the firstdielectric layer, and coupled to the end portion of the first conductivecolumn.
 3. The memory device of claim 1, further comprising: a topelectrode disposed above the second dielectric layer, and coupled to theother end of the shell portion of the second conductive column.
 4. Thememory device of claim 1, wherein the shell portion of the firstconductive column structure has a cross-sectional area of about 1 to 10nanometers.
 5. The memory device of claim 1, wherein the shell portionof the first conductive column structure comprises an inner boundary andan outer boundary that each form a circumference of a circular shapewhen viewed from top.
 6. The memory device of claim 1, wherein the shellportion of the first conductive column structure comprises an innerboundary and an outer boundary that each form a circumference of apolygonal shape when viewed from top.
 7. The memory device of claim 1,further comprising: a second phase change material layer formed over thefirst dielectric layer, wherein a lower boundary of the second changematerial layer contacts at least a second portion of the other end ofthe shell portion of the first conductive column.
 8. The memory deviceof claim 7, wherein at least one of the first and second phase changematerial layers has a circular shape, a polygonal shape, or acircumferential shape when viewed from top.
 9. A memory device,comprising: a bottom electrode formed in a first dielectric layer; aphase change material layer formed in a second dielectric layer; and aheater structure formed in a third dielectric layer and extendingentirely through the third dielectric layer between the bottom electrodeand the phase change material layer, wherein the heater structure linesa trench thereby causing a first portion of the heater structure tocontact the phase change material layer at a first end and wrap adielectric material directly disposed below the phase change materiallayer, wherein the heater structure further comprises a second portioncoupled to a second end of the first portion and disposed below thewrapped dielectric material, the second end being opposite the firstend, and wherein the first portion of the heater structure comprises aninner boundary and an outer boundary that each form a circumference of acircular shape when viewed from top.
 10. The memory device of claim 9,wherein the heater structure is formed of a conductive material selectedfrom at least one of: TaN, TiN, TiAlN, and TiW.
 11. The memory device ofclaim 9, wherein the first portion of the heater structure has across-sectional area of about 1 to 10 nanometers.
 12. The memory deviceof claim 9, further comprising: a top electrode disposed above andcoupled to the phase change material layer.
 13. The memory device ofclaim 9, wherein the first portion of the heater structure comprises aninner boundary and an outer boundary that each form a circumference of apolygonal shape when viewed from top.
 14. The memory device of claim 9,wherein the phase change material layers has a circular shape, apolygonal shape, or a circumferential shape when viewed from top.
 15. Amemory device, comprising: a first conductive column structure extendingentirely through a first dielectric layer, wherein the first conductivecolumn structure comprises a shell portion wrapping a core structurefilled with a dielectric material and an end portion that is coupled toa first end of the shell portion and disposed below the core structure,wherein the shell portion comprises a conductive layer; a first phasechange material layer formed over the first dielectric layer, wherein alower boundary of the first phase change material layer contacts atleast a first portion of a second end of the shell portion, the secondend being opposite the first end; a second dielectric layer disposedabove the first phase change material layer; and a second conductivecolumn structure extending through the second dielectric layer, whereinthe second conductive column structure comprises a shell portionwrapping a core structure filled with a dielectric material and an endportion that is coupled to one end of the shell portion and disposedbelow the core structure, wherein an upper boundary of the first phasechange material layer contacts the end portion of the second conductivecolumn.
 16. The memory device of claim 15, further comprising: a bottomelectrode disposed below the first dielectric layer, and coupled to theend portion of the first conductive column.
 17. The memory device ofclaim 15, further comprising: a top electrode disposed above the seconddielectric layer, and coupled to the other end of the shell portion ofthe second conductive column.